System and method for controlling the length of a discrete segment of a continuous web of elastic material

ABSTRACT

In a system and method for controlling the length of a discrete segment of an elastic web, a wound off tension of the web is determined during unwinding from a wound roll. The unwound web is delivered to a processing station while being maintained in tension. A discrete segment of the web is transported away from the processing station for at least a time t wherein the discrete segment decreases in length to a recovered length. The recovered length is predicted based at least in part on the wound off tension and in response to the predicted recovered length, at least one of the following is controlled: 1) the speed at which the web is delivered to the processing station, 2) the tension in the continuous web as it is delivered to the processing station, and 3) the length of the discrete segment at the processing station.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 11/849,038, filed Aug. 31, 2007, which is hereby incorporatedby reference in its entirety.

FIELD OF INVENTION

This invention relates generally to the handling of continuous webs ofelastic material, and more particularly to a system and method forcontrolling the length of a web segment of the continuous web of elasticmaterial.

BACKGROUND

A number of different handling processes are used to process continuouswebs of elastic material into defined segments, such as discrete webscut from a continuous web for subsequent processing. For example, suchdiscrete webs of elastic material are commonly used as components in theassembly of diapers, training pants and other disposable absorbentgarments. As a further example, the side panels of such absorbentgarments are typically discrete webs of elastic material. In general,the absorbent garment manufacturing line in which the discrete webs areused comprise a pre-wound roll of the continuous elastic material thatis unwound by a suitable drive mechanism and fed (often through variousstations of the manufacturing line) to a cutting station at which theweb is cut sequentially into discrete webs of the elastic material.Typically the continuous web is held in tension as it is transportedfrom the wound roll to the cutting station so that the web is elongatedto some extent. The discrete webs are then transported away from thecutting station to another station of the manufacturing line at whichthe discrete webs are placed on and assembled with other components ofthe absorbent garment being formed.

Research has shown that the stretchability (i.e., the ability of the webto elongate under tension) of a continuous web that is pre-wound on awound roll of the web material may vary throughout the roll (i.e., fromthe beginning to the end of the roll, or throughout the radius of theroll), and from one roll to the next. For example, if a discrete web iscut from a segment of the beginning of a roll under a particular tension(e.g., at the cutting station), and another discrete web is later cutfrom a segment elsewhere (e.g., the middle or the end) on the roll underthat same tension, the cut lengths may be different due to variantstretchability at different segments of the continuous web.

Accordingly, existing elastic web handling processes and, in particular,absorbent garment manufacturing lines often include some type of controlsystem and/or method for detecting the cut length of the discrete websand correcting the cut length when cut length errors are detected. Forexample, a feedback-type control system relies on a cut length error(i.e., the difference between a measured cut length of the discrete weband a target cut length) to determine the magnitude of a processingcorrection. Other known systems and methods utilize what is referred toas a feed-forward control system that predicts what the cut length willbe based on conditions of the web prior to cutting, and when necessaryadjusts the feed rate, web tension or other properties based on thepredicted cut length. For example, in one such process registrationmarks on the continuous web are used to measure the distancetherebetween just prior to cutting and to predict the cut length of thediscrete webs based on this measurement. By comparing the predicted cutlength to a target cut length, the manufacturing line is adjusted by thecontrol system to change the predicted cut length so as to more closelymatch the target cut length.

However, when dealing with an elastic web that is under tension (andmore particularly, stretched) upon being fed to the cutting station, thediscrete webs will retract, or recover after being cut since they are nolonger under tension. In particular, due to elastic effects the discretewebs will recover in some measure relatively quickly following cutting,and due to visco-elastic effects will further recover more slowly sothat at a time t after being cut the length (i.e., the machine directiondimension) of the discrete web will have decreased. A similar effect isexperienced in defined segments of the continuous web, such as betweenregistration marks, where processing of the continuous web involvesstretching the web and subsequently reducing or removing the stretchingforces from the continuous web.

In prior web handling processes such as those described above, the “cutlength” or “segment length” measured or predicted (and relied upon) bythe control system manufacturing line is the length of continuous webthat is actually cut at the cutting station, or other processed at aparticular station in its stretched condition, not the length followingrecovery under reduced or zero tension some time t after cutting orprocessing. Thus, such a control system does not take into account therole that changes in elastic and visco-elastic effects have on thediscrete webs or web segments as they are transported from the cuttingor processing station to further processing stations. Instead, aparticular uniform amount of recovery of the discrete web is presumed.

It is known, though, that the pre-wound continuous web of elasticmaterial is subjected to both radial and circumferential stress thatvaries throughout the wound roll of web material, typically due toexisting winding processes and the changing size of the roll from thefirst wind to the last. Because the continuous web may remain in thiscondition for a prolonged period of time before being used in theabsorbent garment manufacturing line, the visco-elastic properties ofthe web can change (e.g., resulting in the web being partially or whollyset in a more elongated condition) and indeed may vary substantiallythroughout the radius of the roll of web material, or from one roll tothe next. Thus, after a time t following cutting (or segment processingbetween registration marks), discrete webs cut from one segment of thewound continuous web may not recover as much as, or may recover morethan, discrete webs cut from another segment of the wound continuousweb. This can occur even if the cutting length at the cutting station isthe same for the discrete webs because the permanent or partial set inthe wound web varies throughout the web but the tension in the web atthe time of cutting is generally uniform.

There is a need, therefore, for a system and method of controlling thelength of a discrete web of elastic material at a time t followingcutting of the discrete web from a wound roll of continuous web, and/orcontrolling the length of a segment of a continuous web of elasticmaterial at a time t following a particular processing step, and moresuitably such a system and method which takes into account both thevisco-elastic and elastic conditions of the continuous web of materialprior to cutting or prior to the particular processing step.

SUMMARY

In one embodiment, a method of controlling the length of a discretesegment of an elastic web in a web handling system generally comprisesunwinding a continuous web of elastic material from a wound roll of thecontinuous web. A wound off tension of the continuous web is determinedas the continuous web is being unwound from the wound roll. The unwoundcontinuous web is delivered in a machine direction from the wound rollto a processing station while maintaining the web in tension for atleast part of the distance traveled by the web from the wound roll tothe processing station, with a discrete segment of the web having asegment length at the processing station. The discrete web istransported away from the processing station along the machine directionfor at least a time t wherein the discrete segment decreases in machinedirection length from the segment length to a recovered length afterleaving the processing station. The recovered length of the discretesegment at the time t after leaving the processing station is predictedbased at least in part on said wound off tension of the continuous web.In response to the predicted recovered length of the discrete segment,at least one of the following is controlled: 1) the speed at which thecontinuous web is delivered from the wound roll to the processingstation, 2) the tension in the continuous web as the web is deliveredfrom the wound roll to the processing station, and 3) the segment lengthof the discrete segment at the processing station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of one embodiment of a web handling system forcontrolling the length of a discrete web of material cut from acontinuous web of elastic material;

FIG. 1A is a schematic of an unwind spindle, wound roll of web materialand a wound off tensioning monitoring system of the web handling systemof FIG. 1;

FIG. 2 is a flow diagram according to one embodiment of a method ofcontrolling the length of a discrete web of material at a time t afterbeing cut from a continuous web of elastic material;

FIG. 3 is a flow diagram according to a second embodiment of a method ofcontrolling the length of a discrete web of material at a time t afterbeing cut from a continuous web of elastic material;

FIG. 4 is a plot of recovery curves of the measured strain versus timeat zero tension (i.e., after the simulated cut of a discrete segmentfrom a continuous web) for a simulated processing of a continuous web ofelastic material; and

FIG. 5 is the same plot as FIG. 4 but over a shorter time duration afterthe simulated cut.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION

With reference now to the drawings, FIG. 1 is a schematic diagram of oneexample of a web handling system, generally indicated at 21, forcontrolling the length of discrete webs 23 a of elastic material at atime t after the webs are cut from a continuous web 23 b of elasticmaterial, and more particularly from a wound roll 25 of such acontinuous web of elastic material. The illustrated web handling system21 suitably feeds a disposable absorbent garment manufacturing line (aportion of which is indicated generally at 29 in FIG. 1) in whichvarious components of the garment are assembled together as thecomponents, and hence the garment at various stages of assembly thereof,are moved through the manufacturing line in a machine direction MD.Examples of such disposable absorbent garments include, withoutlimitation, diapers, training pants, adult incontinence products,feminine care products and the like. In the illustrated embodiment, thediscrete webs 23 a formed by the web handling system 21 are used as sidepanels of a pair of training pants and are fastened to the movingtraining pants assembly at a side panel fastening station 51 of themanufacturing line 29.

It is understood, however, that the web handling system 21 and methodsdescribed herein may be used by itself to produce discrete webs, or tofeed a manufacturing line for making articles other than disposableabsorbent garments, and remain within the scope of this invention. Asused herein, the term “machine direction” refers to the direction inwhich the web 23 b (and discrete webs 23 a after cutting) are movedthrough the web handling system 21. The term “cross-machine” directionrefers to a direction that is generally orthogonal to the machinedirection MD and in the plane of the web 23 a, 23 b.

While the system and methods illustrated and described herein are for aweb handling system 21 in which a continuous web is cut into discretesegments of web material, it is also understood that the web handlingsystem and methods described herein may be used to control the length ofparticular segments (e.g., discrete segments) of a continuous web ofelastic material, such as between registration marks or other markers ona continuous web, following processing of the web during which the webis tensioned and subsequently released in whole or in part from suchtension. Accordingly, the term “discrete segment” as used herein istaken to refer to a cut segment of web material cut from a continuousweb or to a defined segment of web material (e.g., between registrationmarks or other markers) along a continuous web.

Suitable elastic materials from which the web 23 a, 23 b may be formed,as well as one example of a suitable process for incorporating elasticside panels into an absorbent garment, are described in the followingU.S. Pat. Nos. 4,940,464 issued Jul. 10, 1990 to Van Gompel et al.;5,224,405 issued Jul. 6, 1993 to Pohjola; 5,104,116 issued Apr. 14, 1992to Pohjola; and 5,046,272 issued Sep. 10, 1991 to Vogt et al.; all ofwhich are incorporated herein by reference. As an example, suitableelastic materials include a stretch-thermal laminate (STL), aneck-bonded laminate (NBL), a reversibly necked laminate, or astretch-bonded laminate (SBL) material. Methods of making such materialsare well known to those skilled in the art and described in U.S. Pat.No. 4,663,220 issued May 5, 1987 to Wisneski et al.; U.S. Pat. No.5,226,992 issued Jul. 13, 1993 to Morman; and European PatentApplication No. EP 0 217 032 published on Apr. 8, 1987 in the names ofTaylor et al.; all of which are incorporated herein by reference.

As used herein, the term “stretchable” refers to a material that may beextensible and/or elastic. That is, the material may be extended,deformed or the like, without breaking, and may or may not significantlyretract (i.e., recover) after removal of an elongating force. The term“elastic” refers to that property of a material where upon removal of anelongating force the material is capable of substantially recovering itsoriginal size and shape or exhibits a significant retractive force. Asused herein, an elastic material is intended to refer to a material thatexhibits elastic and/or viscoelastic behavior. The term “viscoelastic”is used herein to refer to that property of a material which is viscousbut which also exhibits certain elastic properties such as the abilityto store energy of deformation, and in which the application of a stressgives rise to a strain that approaches its equilibrium value slowly.

The web handling system 21 suitably includes an unwind spindle 27(broadly, an unwind device) on which the wound roll 25 of the continuousweb 23 b of elastic material is mounted. The illustrated system 21particularly includes a second unwind spindle 27 and another wound roll25 of continuous web 23 b of elastic material. With this arrangement,when one of the rolls 25 is completely unwound and in need ofreplacement the system 21 draws from the other wound roll while theunwound roll is being replaced. It is understood, however, that a singleunwind device and wound roll 25 may be used without departing from thescope of this invention. It is also contemplated that two or more webs23 b may be drawn from respective wound rolls and laminated or otherwisesecured together to form a continuous web of elastic material prior tothe web being cut into discrete webs 23 a.

A suitable drive mechanism, such as in the form of a rotatably drivendrive roll 31 operates to draw the continuous web 23 b from the woundroll 25 (thereby unwinding the wound roll) to move the web in themachine direction MD along a first path P1 of the system 21. The unwindspindle 27, according to one embodiment, may also be driven. As thecontinuous web 23 b is unwound from the wound roll 25, it is drawn alongthe path P1 over a series of guide rolls 33 (also sometimes referred toas stationary rolls, or idler rolls) and then over a dancer roll 35(broadly, a web tension control) before reaching the drive roll 31. Adancer roll 35 is commonly used to control tension in a moving webwithin a predetermined range of tensions. For example, while the webtension is intended to remain generally constant, it may vary due tofactors such as non-uniform web properties, uneven wound rolls or webmisalignment, speed changes in the drive roll and other factors. Thedancer roll 35 may also be used for monitoring the tension in the web 23b as the web is drawn from the wound roll 25 to the drive roll 31 (e.g.,based on the pre-determined tension range within which the dancer rollis initially set to maintain the web in tension).

It is contemplated that other web tension controls may be used tocontrol the tension in the moving web 23 b after the web is drawn fromthe wound roll 25. For example, a festoon (not shown) may be usedinstead of, or in addition to, the dancer roll 31 to control (includingmonitor) the tension in the web 23 b.

The rotational speed of the drive roll 31 generally determines themachine direction MD speed of the web 23 b as it moves along the path P1from the wound roll 25 to the drive roll. Tension in the continuous web23 b along the path P1 is also at least in part a function of therotational speed of the unwind spindle 27 if the spindle is driven(i.e., a function of the differential between the drive roll rotationalspeed and the driven speed of the unwind spindle). Where the unwindspindle 27 is undriven (i.e., generally free to rotate), the tension inthe moving web 23 b along the path P1 is a function of the rotationalspeed of the drive roll 31 and the inertia of the wound roll 35 andunwind spindle.

A vacuum feed roll 37, located downstream from the drive roll 31 in themachine direction MD of the system 21, is rotatably driven to furtherdraw the continuous web 23 b in the machine direction along a path P2from the drive roll to the feed roll. Additional guide rolls 39 arepositioned along the path P2 along with a load cell 41 used in aconventional manner to monitor the tension in the web 23 b as the web isdrawn along the path P2 from the drive roll 31 to the vacuum feed roll37. The tension in the web 23 b along the path P2 is generally afunction of the rotational speed differential between the driven vacuumfeed roll 37 and the drive roll 31. It is contemplated that a suitabletension control, such as another dancer roll, a festoon or othersuitable control may also be disposed intermediate the drive roll 31 andthe vacuum feed roll 37 instead of or in addition to the load cell 41.

Driven rotation of the vacuum feed roll 37 feeds the continuous web 23b, still under tension, to a cutting station, indicated generally at 43,of the web handling system 21. The cutting station 43 suitably comprisesa knife roll 45 and a rotatably driven anvil roll 47, with one or morecutting mechanisms (e.g., cutting blades) disposed on the knife roll forcutting the continuous web 23 b into discrete webs 23 a (broadly,discrete segments) at regular intervals. That is, the length of thediscrete web 23 a at the cutting station (referred to further herein asthe “cut length” of the discrete webs of elastic material) is generallydependent on the driven rotational speed of the anvil roll 47, thevacuum level of the anvil roll and the speed of the feed roll 37, andwhere more than one anvil is used it is also dependent on the spacingbetween anvils. Thus, the cut length may be preset by the operator ofthe web handling system 21 by setting the anvil roll 47 rotationalspeed, vacuum level, and/or feed roll rotational speed, or it may becontrolled by a suitable speed control (not shown) based on apredetermined target cut length. The machine direction MD path alongwhich the web 23 b is moved from the vacuum feed roll 37 to the anvilroll 47 is identified as path P3 in FIG. 1.

The term “length” as used in reference to the web 23 b, or discrete web23 a (i.e., discrete segment), of elastic material refers to the lengththereof in the machine direction MD, i.e., the direction in which theweb is stretched prior to and then retracted subsequent to cuttingand/or processing. The length does not necessarily refer to the longestplanar dimension of the discrete web 23 a after cutting (or discretesegment of a continuous web after processing). For example, for someside panels the continuous web 23 b is moved in the machine direction MDsuch that immediately after cutting the longer dimension is in thecross-machine direction (i.e., the width of the web as the web isdelivered to the cutting station 43). In other words, the cut length isshorter than the width of the web at the time of cutting. The discreteweb 23 a is subsequently rotated before being placed on the trainingpants assembly so that as placed on the assembly the longer dimension ofthe discrete web extends lengthwise of the pants. The drive roll 31,vacuum feed roll 37 and anvil roll 47 together broadly define herein adelivery system that is operable to unwind the continuous web 23 b fromthe wound roll 25 and deliver the continuous web to the cutting station43.

A vacuum transfer roll 49 receives the discrete webs 23 a from the anvilroll 47 after cutting and transfers the discrete webs onto a suitabletransfer device, such as a vacuum conveyor 50, for transport in themachine direction MD away from the cutting station. Additional transferdevices (not shown) further transport the discrete webs 23 a to themanufacturing line 29, and more suitably in the illustrated embodimentto a side panel fastening station 51 where the discrete webs are placedon and assembled with (e.g., adhered or bonded to) other components ofthe absorbent garment assembly 52 moving along the manufacturing line.For some absorbent garments, such as training pants, the absorbentgarment assembly 52 is further moved by the manufacturing line 29 to agarment fastening station 53 where the side panels at front and backwaists of the garment are secured together to form a three-dimensionalarticle having a continuous waistline in the manner of underwear.

One or more detection or monitoring systems for detecting anddetermining the length (and hence subsequent recovery) of the discretewebs 23 a at particular locations or at a time t after cutting aredisposed at predetermined locations, such as intermediate the vacuumtransfer roll 49 of the web handling system 21 and the side panelfastening station 51 of the manufacturing line 29. For example, in theillustrated embodiment a first inspection system 55, and more suitably avision inspection system, is located downstream (in the machinedirection MD) from the vacuum transfer roll 49 at a first distancetherefrom and a second inspection system 57, also more suitably a visioninspection system, is located downstream from the first inspectionsystem such as at or adjacent to the side panel fastening station 51 todetermine the length of the discrete web 23 a as the web approaches thefastening station or just after the discrete web (i.e., the side panelmaterial) has been secured to the moving absorbent garment assembly 52.

The machine direction MD distances between the various components andstations of the web handling system 21 and manufacturing line 29illustrated in FIG. 1 are not necessarily to scale but are otherwisegenerally indicative of the relative spacing between such components.Thus, given the speed of the moving web 23 b (which may be monitored byvarious speed sensors, not shown, disposed along the paths P1, P2 or atother locations along the web handling system 21) and the known machinedirection MD distance between any two stations or system components, thetime that the web takes to reach any particular station or component maybe readily determined. The time t may also, or alternatively, bemonitored or detected by suitable timing devices.

During operation of the illustrated web handling system 21, thecontinuous web 23 b may experience various levels of tension for certainperiods of time prior to reaching the cutting station 43 (or otherprocessing station), each of which has a bearing on the elastic andvisco-elastic behavior of the discrete webs 23 a (i.e., discretesegments) after leaving the cutting station (i.e., the processingstation). For example, while on the wound roll 25, the continuous web 23b is subjected to both radial and circumferential stresses thatcontribute to what is referred to herein as a wound off tension (i.e.,the tension in the continuous web as the web is unwound from the woundroll during operation).

In one particularly suitable embodiment the wound off tension may bedetermined by a suitable wound off tension monitoring system, generallyindicated as 61 in FIG. 1A, as the web 23 b is unwound from the woundroll 25. For example, the illustrated wound off tension monitoringsystem 61 comprises a load cell 63 (similar to the load cell 41 used todetermine the tension in the web along path P2 in the system 21 ofFIG. 1) located within the wound roll 25 between the outermost wind andthe immediately underlying wind of the continuous web 23 b. The loadcell 63 measures the tension in the outermost wind (which is about to bewound off from the roll 25) in pounds. Dividing this tension by theaverage thickness and average width of the web determines the wound offstress, in pounds per square inch, of the continuous web.

In alternative embodiments, the wound off tension may be pre-determined,such as during initial winding of the continuous web 23 b onto the woundroll 25 or on a separate winding system (not shown) disposed offlinefrom the web handling system 21, to develop a wound off tension profilein which the wound off tension is recorded as a function of the radiusof the wound roll 25 or as a function of the linear location along thelength of the continuous web 23 b on the wound roll. In such anembodiment, the wound off tension monitoring system 61 may comprise asuitable device (not shown) for monitoring the radius of the wound roll25 and/or the linear location of the web 23 b along the wound roll.

The continuous web 23 b is subsequently subjected to a first movingtension for the period of time during which the web is drawn along thepath P1 from the wound roll 25 to the drive roll 31, and is subjected toa second moving tension for the additional period of time during whichthe web is drawn along the path P2 from the drive roll to the vacuumfeed roll 37. The continuous web 23 b is also subjected to a thirdmoving tension, based on a speed differential between the anvil roll 47and the vacuum feed roll 37, as well as the respective vacuum levels ofthe vacuum feed roll and the anvil roll, for a relatively short periodof time as the web moves along the path P3 from the vacuum feed roll tothe anvil roll. It is understood that once the web 23 b is cut into thediscrete webs 23 a there is a substantially reduced tension (and in someembodiments, zero tension) applied to each discrete web (i.e., thediscrete web of elastic material is allowed to recover) depending onsubsequent processing of the web after cutting, such as, for example,the level of vacuum applied to the web by a vacuum conveyor thattransfers the discrete webs away from the cutting station.

With reference back to FIG. 1, the illustrated web handling system 21further comprises a control system 71 for controlling operation of theweb handling system. The control system 21 may be part of, or mayprovide input to and receive feed back from, a manufacturing controlsystem (not shown) of the manufacturing line 29 to which the discretewebs are supplied for incorporation into the absorbent garment. Thecontrol system 71 is suitably in communication with the variousoperating components of the system 21 and is capable of monitoring andadjusting (or causing to be adjusted) various operating parameters ofthe system 21 (as indicted by the arrows drawn between the controlsystem and the respective operating components in FIG. 1) such as thespeeds of the drive roll 31, vacuum feed roll 37 and other transferdevices to thereby control the machine direction MD speed of thecontinuous web 23 b (to the cutting station 43) and discrete webs 23 a(downstream of the cutting station); the tension in the web 23 b alongpaths P1, P2 and P3, and/or the cut length of the discrete webs at thecutting station. The control system 71 also suitably communicates withand receives input from the wound off tension monitoring system 61, theload cell 63 and the inspection systems 55, 57. The control system 71may suitably comprise a control circuit, a computer that executescontrol software, a programmable logic controller and/or other suitablecontrol devices.

In accordance with one embodiment of a method for controlling the lengthof the discrete web 23 a (i.e., a discrete segment) of elastic materialat a time t after the web is cut from the continuous web 23 b of theelastic material (or, more broadly, at a time t after the discretesegment is processed at a particular processing station), the controlsystem 71 is used to control the various operating components of the webhandling system 21 so as to control the length of the discrete web afterit is cut (i.e., after the discrete segment leaves the processingstation). More suitably, the control system 71 is configured to controlthe length of the discrete web 23 a according to a feed-forward typecontrol method. According to such a method, a recovered length of thediscrete web 23 a at a time t after it is cut from the continuous web 23b of material is predicted at least in part as a function of the woundoff tension of the wound roll 25 and of the time t at which a targetrecovered length is to be achieved.

For example, in the illustrated embodiment the length of the discreteweb 23 a is predicted (based on the wound off tension) at a time t aftercutting, wherein the time t corresponds to the location of the sidepanel fastening station 51 where the side panels overlay and are securedto the moving absorbent garment assembly 52. The time t corresponding tothis location is simply a function of the machine direction MD distancefrom the cutting station 43 to the side panel fastening station 51 andthe speed at which the discrete webs 23 a are moved therebetween, whichmay be a manual input to the control system or may be monitored by thecontrol system 71.

Even more suitably, the length of the discrete web 23 a at a time tafter it is cut from the continuous web 23 a of elastic material at thecutting station 43 is predicted according to the following algorithmwhich is programmed into the control system 71:

Strain=(C ₀ +C ₁ *τ+C ₂*τ²)*[J ₀ +J ₁ *e ^((t/T1)) +J ₂ *e ^((t/T2))]

where;

τ=the wound off tension (lbs.)

t=time after cut (seconds)

Ji are coefficients based on a recovery curve of the discrete web, whichis a curve fit of the measured length of a discrete web after cut versustime t after the cut for the particular web handling system parametersat which the wound roll is processed;

Ci are coefficients based on the spread of multiple recovery curves fordifferent wound off tensions (i.e., each wound off tension generates adifferent recovery curve and the Ci coefficients model the spreadbetween these recovery curves); and

Ti are time related constants based on the different curve fit patternsat different times after the cut.

In one particularly suitable embodiment, the coefficients Ji, Ci and Tiare constants determined by conducting data collection and curve fittingoff-line (i.e., other than on the manufacturing line 29 and moresuitably other than on the web handling system 21). For example, byknowing (or assuming) 1) the speed at which the continuous web 23 bmoves along the various paths P1, P2, P3, 2) the distance of each ofthese paths, and 3) the various tensions to which the continuous web issubjected as the web moves along each of the paths, and assuming thatthese are held constant, the data for determining the coefficients forthe above algorithm (as they relate to the particular web speeds,distances and tensions) can be measured using suitable off-linemeasuring equipment (not shown). Without limitation, the following isone example of how these coefficients may be determined offline.

Example 1

The following example determines the coefficients Ji, Ci and Ti using anoffline data collection process. The data collected in this exampleassumes a web handling system 21 substantially as set forth above andillustrated in FIG. 1 in which the discrete webs 23 a of elasticmaterial are used as side panels that are subsequently secured to amoving absorbent garment assembly 52 at a side panel fastening station51 to further assemble the absorbent garment. The continuous web 23 b ofelastic material for this example is a continuous web of verticalfilament material having a basis of weight of about 108.87 grams persquare meter (gsm).

A vertical filament laminate (VFL) is a composite material having atleast two layers in which one layer is a gatherable layer and the otherlayer is an elastic layer. The layers are joined together when theelastic layer is extended from its original condition so that uponrelaxing the layers, the gatherable layer is gathered. The composite maybe stretched to the extent that the non-elastic material gatheredbetween the bond locations allows the elastic material to elongate. Onetype of vertical filament laminate is disclosed, for example, by U.S.Pat. No. 6,916,750 to Thomas et al., the content of which isincorporated herein by reference in its entirety. In particular, the VFLused for this example is that used as side panel material for trainingpants made by Kimberly-Clark Worldwide, Inc., Neenah, Wis.

The web 23 b has a uniform caliper (i.e. thickness) of about 0.03 inchesand a uniform width of about 12.13 inches. The continuous web 23 b isassumed (based on actual runtime data from the web handling system 21 orestimated based on desired operating parameters such as web speed andtension to achieve a cut length at the cutting station 43 of about 3.414inches) to have 1) a first tension along path P1 of about 0.83 lbs. fora period of about 10 seconds (e.g., as the web moves from the wound roll25 to the drive roll 31), 2) a second tension along path P2 of about 1.1lbs. for a period of about 4 seconds (e.g., as the web moves from thedrive roll to the vacuum feed roll 37, and 3) a third tension along pathP3 of about 1.54 lbs. for a period of about 0.5 seconds (e.g., as theweb moves from the vacuum transfer roll to the anvil roll 47 forcutting).

Five different data collection runs are made, with the wound off tensionbeing the only variable that changed for each run. In particular, thewound off tension is 0.5, 1.0, 1.5, 2.0 and 2.5 lbs. for each respectiverun. It is understood, however, that more or less runs may be made byincreasing or decreasing the number of wound off tension increments, orby increasing the overall range of the wound off tension.

Suitable measuring equipment comprises conventional modulus test machinein which a sample length of the web material is held fixed at one endand is attached to a rail mounted, low friction slide. The tensionmachine is capable of controlling the position of the slide on the railto adjust the tension, and hence the elongation, in the web. For eachdata collection run, the sample is cut from the roll and allowed to cometo equilibrium in an untensioned state. The web is then tensioned inaccordance with the simulated wound off tension for that run (e.g., 0.5lbs. for the first run, 1.0 lbs. for the second run, etc.) and held atthis tension for a period of one-hour to simulate the effects of theradial and circumferential stresses experienced by a wound web forprolonged periods. The slide is then adjusted to tension the web at thefirst tension (0.83 lbs.) for 10 seconds, then at the second tension(1.1 lbs.) for 4 seconds, and finally at the third tension (1.54 lbs)for 0.5 seconds to simulate movement of the web through the web handlingsystem 21 from the wound roll 25 to the cutting station 43.

The slide is then released to move freely on the tension machine railsso that no tension is applied to the web. The web is thus allowed torecover in order to model the elastic and visco-elastic behavior of thediscrete webs 23 a after being cut at the cutting station 43. Therecovered length of the web (and more suitably the change in length, orshrinkage of the web, reported as strain) is periodically monitored andrecorded, e.g., every 10 seconds, for a total period of 60 seconds. Theprocedure is conducted for each of the other four runs to model theother wound off tensions.

FIG. 4 is a set of recovery curves, overlaid curve fits, of the measuredstrain versus time at zero tension (i.e., after the simulated cut) foreach of the runs. FIG. 5 is the same plot but over a shorter timeduration after the simulated cut. The coefficients Ji, Ci and Ti aredetermined from the curve fits of the recovery curves for each wound offtension and from the spread between the curve fits. Any conventionalcurve fitting software may be used to curve fit the data and todetermine the needed coefficients.

Inserting these coefficients into the above algorithm yields analgorithm that can used to model the behavior of the discrete webs 23 a(i.e., to predict the length, such as the recovered length, of thediscrete webs) formed by the operating web handling system at a time tafter the web is cut from the tensioned continuous web 23 b at thecutting station 43. Using this algorithm, the recovered length of thediscrete web 23 a at a time t after cutting is thus a direct function ofthe wound off tension of the wound roll 25 and of the time t after thediscrete web is cut at the cutting station 43. The recovered length ofthe discrete web 23 a, using the algorithm, is also indirectly afunction of the particular operating parameters (i.e., web speeds,continuous web tensions and cut length) used in determining thecoefficients (the constants) of the algorithm.

In the illustrated embodiment, an operator 73 uses a suitable inputdevice 75 to input parameters needed by the control system 71 to controlthe recovered length of the discrete webs 23 a at a time t aftercutting. The input device 75 in this instance is a computer keyboardassociated with a personal computer (PC) system that is part of orinterfaces with the control system 71 of the web handling system 21.

Input supplied to the control system 71 by the operator 73 includes, ata minimum, a target recovered length of the discrete web 23 a at apredetermined location downstream of the cutting station 43, such as theside panel fastening station 51 in the illustrated embodiment, and thecoefficients, or constants to be used in the above algorithm forpredicting the recovered length of the discrete web at the predeterminedlocation. Additionally, the operator 73 may input a suitable tolerancerange for the recovered length, i.e., the acceptable range of recoveredlengths of the discrete webs 23 a at the predetermined locationdownstream of the cutting station 43. Additional input may also includethe web 23 b caliper and width.

A distance of the predetermined location at which the recovered lengthof the discrete web 23 a is to be predicted may be manually input by theoperator 73, or it may be measured by suitable monitoring devices (notshown) of the web handling system 21 and/manufacturing line 29. Thecontrol system 71 may determine the time t after cutting thatcorresponds to the predetermined location, such as by determining theweb speed of the discrete webs 23 a from the cutting station 43 to thepredetermined location downstream therefrom and using the web speed anddistance to determine the time t to travel this distance. Alternatively,the control system may determine the time t to reach the predeterminedlocation using suitable monitoring systems (not shown) It alsocontemplated that the operator 73 may instead directly input the time tat the input device 75 without departing from the scope of thisinvention.

With reference to FIG. 2, the above input is communicated to the controlsystem at step 101 in accordance with one method for controlling therecovered length of the discrete web 23 a after cutting (broadly, afterleaving a particular processing station). Where an active wound offtension monitoring system 61 is provided as illustrated in FIG. 1A, thewound off tension is periodically determined by the monitoring system,such as about every 10 seconds for example, and the data is relayed at103 to the control system 71. Alternatively, a predetermined data tableof wound off tension to wound roll radius (or other suitable wound rollparameter) may be input to the control system 71 by the operator 73,such as by using the input device 75 or suitable electroniccommunication device. In such an embodiment, a suitable monitoringdevice (not shown) may be used to intermittently determine the radius(or other parameter) of the wound roll 25 and communicate such data tothe control system 71, which then determines the wound off tension basedon the predetermined wound off tension data table.

With the wound off tension and the time t as inputs to the algorithm,the control system 71 uses the algorithm to predict (at step 105) therecovered length of the discrete web 23 a at the time t after thediscrete web is cut from the continuous web 23 b. The control systemthen compares the predicted recovered length to the input targetrecovered length at step 107 to determine a difference therebetween. Ifthe difference between the predicted recovered length and the targetrecovered length is within the input tolerance range, no adjustments tothe operating parameters of the web handling system 21 are needed.

Where the differential falls outside the tolerance range, one or more ofthe web handling system operating parameters, such as one or more of theweb speeds, one or more of the web tensions, and/or the cut length atthe cutting station, is adjusted by the control system 71 at step 109 tothereby adjust the recovered length of the discrete web 23 a at the timet following cutting, i.e., before the segments of the web that are beingwound off from the wound roll are processed (i.e., cut) at the cuttingstation. For example, where the predicted recovered length exceeds thetarget recovered length, one or more of the web speeds may be decreasedand/or one or more of the web tensions may be decreased to shorten thecut length at the cutting station 43 so that the recovered length willalso decrease. Alter-natively, the web speeds and/or tensions may beadjusted to increase the tension (and hence the elongation) in thecontinuous web 23 b at the cutting station 43 (e.g., without necessarilychanging the cut length) to increase the amount of recovery and therebydecrease the recovered length at the time t after the cut.

Where the predicted recovered length is shorter than the targetrecovered length, the web 23 b speeds and/or web tensions and/or cutlength are increased to increase the cut length to thereby increase therecovered length of the discrete webs 23 a, or the web speeds and/ortensions may be adjusted to decrease the tension in the web at thecutting station 43 (while the cut length remains generally unchanged) todecrease the amount of recovery and thereby increase the recoveredlength of the discrete web at the time t after the cut. As the woundroll 25 is unwound, the wound off tension will vary and thus the webhandling system 21 operating parameters may be repeatedly modified bythe control system 71 as the wound off tension changes.

Thus, in accordance with the feed-forward control, the control system 71determines the needed cut length (or discrete length) and/or operatingparameter adjustments while the continuous web is upstream from thecutting station (i.e., the particular processing station of interest),based on the predicted recovered length, so that upon recovery for atime t downstream of the cutting station 43 (i.e., the particularprocessing station) the recovered length of the discrete web 23 a (i.e.,the discrete segment) will match the target recovered length.

It is understood that by changing the web speed and/or the web tensionat one or more of the intervals (paths P1, P2, P3) from the wound roll25 to the cutting station 43, i.e., these parameters may becomedifferent from those used to obtain the data upon which the coefficientsinput by the operator were based. As a result, the coefficients used asinput to the algorithm may not sufficiently model the revised web speedsand/or tensions.

To this end, it is contemplated that coefficient data may be compiled asin the above Example by running the data collection for different webspeeds and tensions along one or more of the paths P1, P2, P3 of the webhandling system. Thus, in a second embodiment of method of controllingthe recovered length of a discrete web after being cutting from acontinuous web of elastic material, illustrated in FIG. 3, the input 201may further include a “look-up” table of coefficients where the propercoefficients to use in the algorithm are a function of the current webspeeds and/or tensions at one or more of the paths P1, P2, P3. That is,the web speeds and/or web tensions may be monitored by the controlsystem 71 and, when changed such as at step 211 in response to thepredicted recovered length being undesirably different from the targetrecovered length, used by the control system to adjust the coefficientsused in the algorithm to further predict 205 the recovered web length atthe time t after cutting.

Alternatively, it is contemplated that the above Example offline datacollection process may be used with one or more of the web tensions(e.g., along the paths P1, P2, P3) as variables and being varied duringdifferent runs of the data collection process along with the wound offtension. As a result, an algorithm that models the recovered length ofthe discrete web 23 a at a time t after cutting as a direct function ofthe wound off tension and one or more of the web tensions along thepaths P1, P2, P3 may be used by the control system 71 to predict therecovered length of the discrete webs at time t after cutting.

It is also contemplated that the control system 71 may operate tocollect additional, real-time data relating the actual recovered length(as measured, for example, by the inspection system 57 at the side panelfastening station 51) at a time t after cutting to at least the woundoff tension of the wound roll. In such an embodiment, real-time curvefits of the data can be made by the control system 71 and the inputcoefficients to the algorithm adjusted accordingly. Such a method allowsfor variations in different webs, i.e., the elastic and viscoelasticbehavior between different webs is accounted for in real-time (i.e.without the need for off-line data collection for each different woundroll of elastic material). Alternatively, or additionally, the actualrecovered length could be used as an input to the control system andused to further determine needed adjustments of the various processparameters.

When introducing elements of the present invention or preferredembodiments thereof, the articles “a”, “an”, “the”, and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including”, and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

As various changes could be made in the above constructions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

1. A method of controlling the length of a discrete segment of anelastic web in a web handling system, said method comprising: unwindinga continuous web of elastic material from a wound roll of saidcontinuous web; determining a wound off tension of said continuous webas said continuous web is being unwound from said wound roll; deliveringthe unwound continuous web in a machine direction from said wound rollto a processing station while maintaining the web in tension for atleast part of the distance traveled by the web from the wound roll tothe processing station, a discrete segment of the web having a segmentlength at said processing station; transporting the discrete segment ofthe web away from the processing station along said machine directionfor at least a time t wherein the discrete segment decreases in machinedirection length from said segment length to a recovered length afterleaving said processing station; predicting, based at least in part onsaid wound off tension of said continuous web, the recovered length ofthe discrete segment at said time t after leaving the processingstation; and controlling, in response to the predicted recovered lengthof the discrete segment, at least one of 1) the speed at which thecontinuous web is delivered from the wound roll to the processingstation, 2) the tension in the continuous web as the web is deliveredfrom the wound roll to the processing station, and 3) the segment lengthof the discrete segment at the processing station.
 2. The method setforth in claim 1 further comprising comparing the predicted recoveredlength of the discrete segment to a predetermined target recoveredlength of the discrete segment at said time t after leaving theprocessing station, the controlling step comprising controlling, inresponse to said comparison of the predicted recovered length of thediscrete segment to the predetermined target recovered length of thediscrete segment, at least one of 1) the speed at which the continuousweb is delivered from the wound roll to the processing station, 2) thetension in the continuous web as the web is delivered from the woundroll to the processing station, and 3) the segment length of thediscrete segment at the processing station.
 3. The method set forth inclaim 2 wherein the comparing step comprises determining the differencebetween the predicted recovered length of the discrete segment and thepredetermined target recovered length of the discrete segment at saidtime t after leaving the processing station, and comparing thedifference therebetween to a target tolerance range for said difference,the controlling step comprising controlling, in response to saiddifference falling outside of said target tolerance range, at least oneof 1) the speed at which the continuous web is delivered from the woundroll to the processing station, 2) the tension in the continuous web asthe web is delivered from the wound roll to the processing station, and3) the segment length of the discrete segment at the processing station.4. The method set forth in claim 1 wherein the step of delivering theunwound continuous web in a machine direction from said wound roll tosaid processing station comprises maintaining the continuous web ofelastic material in tension for substantially the entire distance fromthe wound roll to the processing station.
 5. The method set forth inclaim 4 wherein the tension in said continuous web of elastic materialis non-uniform along the distance from the wound roll to the processingstation.
 6. The method set forth in claim 1 wherein the predicting stepcomprises predicting a recovered length of the discrete segment at saidtime t after leaving the processing station based at least in part onsaid wound off tension of said continuous web and said time t after thediscrete segment leaves the processing station.
 7. The method set forthin claim 6 wherein the predicting step comprises predicting therecovered length of the discrete segment at said time t after thediscrete segment leaves the processing station based at least in part onsaid wound off tension of said continuous web, the tension of the webalong at least a portion of the distance that the continuous web isdelivered from the wound roll to the processing station, and said time tafter discrete segment leaves the processing station.
 8. The method setforth in claim 1 wherein the wound off tension is determined bymeasuring the tension in the continuous web as it is being wound off ofthe wound roll.
 9. The method set forth in claim 1 further comprisingthe step of determining, prior to unwinding the continuous web from saidwound roll, a relationship between the wound off tension of the woundroll and at least one of the radius of the wound roll and the linearlocation along the wound roll, the step of determining the wound offtension comprising determining said at least one of the radius of thewound roll and the linear location along the wound roll as the woundroll is being unwound and determining the wound off tension based onsaid at least one of the determined radius of and the determined linearlocation along the wound roll.
 10. The method set forth in claim 1wherein the processing station comprises a cutting station, the discretesegment comprising a discrete web cut from the continuous web at saidcutting station and having a cut length at said cutting station, saidtransporting step comprising transporting the discrete web away from thecutting station along said machine direction for at least a time t aftercutting wherein the discrete web decreases in machine direction lengthfrom said cut length to a recovered length after cutting, saidpredicting step comprising predicting, based at least in part on saidwound off tension of said continuous web, the recovered length of thediscrete web at said time t after cutting, and said controlling stepcomprising controlling, in response to the predicted recovered length ofthe discrete web, at least one of 1) the speed at which the continuousweb is delivered from the wound roll to the cutting station, 2) thetension in the continuous web as the web is delivered from the woundroll to the cutting station, and 3) the cut length of the discrete webat the cutting station.
 11. The method set forth in claim 1 furthercomprising the steps of determining an actual recovered length of thediscrete segment at or after said time t after leaving the processingstation, comparing the actual recovered length of the discrete segmentto a predetermined target recovered length of the discrete segment atthe time at which the actual recovered length is determined, andcontrolling in response to said comparison of the actual recoveredlength to the predetermined target recovered length of the discretesegment, at least one of 1) the speed at which the continuous web isdelivered from the wound roll to the processing station, 2) the tensionin the continuous web as the web is delivered from the wound roll to theprocessing station, and 3) the segment length of the discrete segment atthe processing station.